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How to bridge 2 ethernet interfaces from host blade to guest VM

asked 2014-06-27 19:31:07 -0500

rasselin gravatar image

I'm trying to bridge my host's eth0 and eth1 into a vm's eth0 and eth1. I did manage to do it once documented here: (

But I'm not able to reproduce it on a new devstack setup based on stable/icehouse. Regardless, there's gotta be a better way.

Does anyone know the "correct" way to do this?

Here's the extract from the above link:

Configuring the host openstack "provider" to allow access to guest openstack "nodes" with two eth has proved to be trick. e.g host eth0 --> instance eth0 (public network) host eth1 --> instance eth1 (iSCSI network). Nova-network seems to be broken / doesn't support this / I'm not smart enough to follow the docs on doing this: ( . But I did get it working manually: Briefly:

  1. Create an instance vm to setup basic networking within nova (no idea why this step is necessary, but if you skip it, you won't be able to log into instances. But it'd be good to re-confirm if this is really true..perhaps I messed up somewhere)

  2. create the network: nova network-create my_iscsi --fixed-range-v4= --bridge=br_iscsi --bridge-interface=eth1 --multi-host=T

  3. Add eth1 to the bridge: sudo brctl addif br_iscsi eth1

  4. Move the ip from eth1 to br-iscsi sudo ifconfig br_iscsi add sudo ip addr del dev eth1

  5. Update routing tables:
    sudo ip route add dev br_iscsi proto kernel scope link src

  6. (Done within jenkins job) Manually configure eth1 in the instance vm: with the private ip address it's assigned: ifup eth1 (it will get it's ip via nova's dhcp server) Ensure the routing table is correct. e.g. up route add -net dev eth1

My devstack nova setup (for better or worse): local.conf has:











multi_host = True

allow_same_net_traffic = False

send_arp_for_ha = True

share_dhcp_address = True

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I figured out the 1st half of the problem: auto-creation of the bridge interfaces. Investigation notes here: (

Summary: the FLAT_INTERFACE value provided in nova.conf is used by nova-network INSTEAD OF the value passed into: --bridge-interface= !! This was to fix a bug: "Allows heterogeneous networks a la bug 833426"

Workaround is to force the /etc/nova.conf to be an empty string.


My attempt to auto-set this in variable local.conf failed (solutions welcomed), but after running, manually make the change to /etc/nova/nova.conf, and then the above nova network-create will use the specified value in --bridge-interface=

Still need to figure out the routing tables.

rasselin gravatar imagerasselin ( 2014-07-31 15:15:08 -0500 )edit

This blog has the partial answer using neutron. The next part is not posted yet. "DevStack Neutron With ML2, Open VSwitch, VLANs, and Overlay VxLAN Tunnels"

rasselin gravatar imagerasselin ( 2014-08-22 17:53:49 -0500 )edit

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answered 2014-12-25 05:35:07 -0500

Check your /etc/sysctl.conf file and ensure that you have enabled ipv4 forwarding


And try enable MASQUERADE via iptables.

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Asked: 2014-06-27 19:31:07 -0500

Seen: 1,167 times

Last updated: Dec 25 '14